During logging operations, trees are felled, lateral branches trimmed and the top portions removed to produce logs of desired size. A rubber tired or tracked skidder vehicle having a cable winch is used to assemble logs into a bundle and to drag the bundle to a loading area. The logs are attached to a cable generally by chokers looped about the logs or tree trunk and engaged on a sliding bell hook at the rearward end of the main line cable. A cable winch at the forward end of the cable draws the logs forwardly to an area adjacent the rear of the skidder. Bundles are assembled and dragged behind the skidder to a landing area where the logs are loaded upon trucks for transport to a saw-mill or paper mill.
An ecologically destructive method of logging known as "clear-cut logging" is generally used in the belief that it is economically preferable to other methods. In clear-cut logging, all trees in a forest are felled regardless of size but only trees of a desired size and type are actually used to produce logs. Undersized or defective trees which do not meet the desired criterion are felled solely to remove obstacles to the logging operation and are left to rot on the former forest floor.
Conventional skidders are often earth moving vehicles converted for logging operations by installing a cable winch and a fixed frame with a cable sheave on the rear portion of the skidder. Such skidders are large heavy machines which require relatively wide access paths and open areas in which to turn and manoeuvre. A common practice in operating such skidders is to attach chokers to a number of tree stems or logs and then simultaneously draw all the logs toward the skidder with a single cable. Each choker is attached to a sliding bell hook at the end of the main line cable and all logs are drawn together from their individual positions in a fan-like configuration which is called a gathering operation. Such operations require that obstacles be removed in the path of the logs as they are drawn and slide along the forest floor toward the skidder. To reduce handling costs therefore clear cutting is used. Logs are removed from where they have fallen and drawn into a bundle for dragging to a loading area in a single operation. It is generally believed by those practicing clear cut logging that clear cut logging is the most profitable method of harvesting mature trees. Such an approach is becoming increasingly unacceptable due to long term or permanent ecological damage.
Use of such large and heavy conventional skidders is necessary when large numbers of logs are both drawn and dragged by a single skidder. In addition to requiring open areas to operate, conventional skidders tend to cause deep ruts in the forest floor due to excessive machine and load weight. The ruts speed erosion by providing channels for runoff water.
Since logs are dragged behind such skidders, the frictional force of the logs dragging on the forest floor increases the tractive effort required. In most cases, conventional skidders have a fixed arch frame which extends rearward of the skidder's rear axle and wheels. The arch frame supports a cable sheave upon which the cable is reeved. The tensile force exerted by the cable upon the arch frame creates a turning moment which tends to increase the bearing load pressure upon the rear wheels while decreasing the bearing load upon the front wheels. The turning moment may lift the front wheels from the forest floor in many cases reducing operator control and subjecting the skidder to damage. The rear wheels under such heavy loads may form deep ruts and may bog down in soft soil. Spinning wheels when traction is inadequate results in further rutting.
Ecologically clear cut logging has catastrophic consequences. A clear cut area quickly erodes since the forest cover no longer protects the soil and root structures from rain and wind erosion nor from drying in the sun. The rutting caused by conventional skidders creates channels for pooling and runoff of water further aiding erosion. Many forest trees and plants require full or partial shade especially in their early stages of growth. Clear cutting exposes such immature trees to direct sunlight thereby impeding their growth and encouraging other types of vegetation such as scrub to grow. The nature of the forest is immediately and radically altered removing wildlife habitat and imposing a harsh environment which delays or prevents forest regeneration. Streams and rivers having increased silt and particle concentrations from soil erosion become inhospitable to wildlife whose numbers decrease as a result.
Efforts at reforestation have met with limited success for a number of reasons. Clear cutting removes the optimal environment for growth of immature trees which require partial shade and protection from wind. The erosion due to clear cutting is so rapid that critical top soil may be lost before replanted trees develop root structures adequate to maintain the soil's integrity. Reforestation requires extensive organization and capital expenditures since it is labour intensive in remote areas. Governments have generally not demonstrated an unwavering commitment to impose mandatory reforestation since maintaining employment in areas dependent upon the forestry industry is a major political concern.
In days long past, individuals trees were harvested as they matured. Horses were used to skid logs from the dense forest to a river, landing, portable saw-mills, or an access road cut through the forest. Logs were loaded upon sleds or trucks, or floated down rivers to sawmills. Although such methods result in less ecological damage and a sustainable renewable forest resource, modern clear cutting methods are preferred since it is widely believed that no other methods or equipment can produce logs in a cost efficient and profitable manner.
Such short term approaches ignore the cost of ecological damage and the benefits of a renewable forest resource. Clear cutting forces logging operations to continually seek new territories to exploit and to abandon the clear-cut logged area for an indeterminate period until the area is naturally regenerated or is reforested by man.
The invention addresses the foregoing disadvantages of conventional methods and vehicles for skidding timber through the use of a selective tree harvesting method and a novel vehicle.
In accordance with one aspect of the invention, a method is proposed wherein only trees of a selected size are felled and removed from the forest as logs. The surrounding trees which are too immature to be harvested or are defective in some manner or not of a desired species are left standing. A sustainable renewable forest resource is maintained since only access paths and roads of a minimal width need be cut through the forest in order to gain access to the selected trees. As trees mature, they may be harvested using the same paths and roads previously cut.
In accordance with a second aspect of the invention, a compact vehicle is proposed for skidding timber. The compact vehicle may be constructed in practice to be of weight no more than 4 tons (3600 kg.), with a maximum velocity capability of 10 m.p.h. (16 kph) and a naturally aspirated diesel engine of under 45 h.p. This vehicle is relatively small in comparison to conventional skidders as described above and is capable of weaving along a narrow path through the forest. As a result of the novel design of the vehicle, a relatively narrow path may be cut which winds around immature trees, thereby avoiding the necessity of cutting down any more trees than is absolutely necessary for access, and transport of the logs. The vehicle is used therefore, to drag logs out of the dense forest to access roads where conventional larger skidders then operate in conventional manner dragging logs to truck transport. The major portion of the forest is left relatively undisturbed as a result therefore, and may remain as a renewable forest in perpetuity.